The present invention relates to improved scissors, shears and the like, and in particular, to improved high-quality scissors and shears, and an improved method of making them.
Scissors, shears and like tools have included two cooperating members that are interconnected, by a pivot pin, bolt and nut, rivet, screw or the like, at a connection point located between their ends, so that the members can be moved, with "scissors-like" action, between a closed position and an open position. Each of the members have a handle formed at their one end, a shank portion disposed between the handle and the connection point, i.e., the pivot pin, bolt and nut, rivet, screw, etc., and a blade portion disposed between the connection point in their other end. The blade portions and the shank portions each have an inside face and an outside face. The blade portions also include cutting edges which usually extend from adjacent to the connection point to their other ends. The members are generally arranged so that when they are in their closed position, the two inside faces of the blade portions and the two inside faces of the shank portions at least partially overlap and are adjacent to each other.
For may years, the manufacture of conventional, high-quality tools required a number of expensive hand grinding operations and the efforts of skilled experienced artisans to shape, sharpen and polish blades and make sure their cutting edges are in proper alignment.
One of the most critical and time consuming of these hand grinding operations was the grinding of the surface or the "ride" of the inside faces of the shank portions so that when these inside faces are moved into contact with each other, as when the members are moved from their open to their closed position, the blade portions will be biased together so as to provide a satisfactory cutting or shearing action. When the hand grinding operation has been properly done, there only will be a "point contact" or "point of contact" between the cutting edges of the members. The artisans doing this critical hand grinding operation always attempt to grind the inside faces of the shank portions so that this point contact between the cutting edges is initially located near the point of initial intersection between the cutting edges and then moves out, along the cutting edges, to their other distal ends as the members are moved to their closed position. Ideally, this critical hand grinding operation should also impart a desirable "feel" to the tool, i.e., require a constant force to move the members from their open position to their closed position.
If the grinding operation is not done properly, the point of contact between the cutting edges may not occur until the blade portions are moved to their closed position. Rather than cutting materials, the blades will just fold the material over, and the material will force the blades apart so that it just passes between the blades.
Alternatively, the shank portions may be ground too much, so that there is excessive contact between the cutting edges of the blades. This results in a tool having a heavy or hard "feel" that requires increased force to move the members from their open position to their closed position. In addition, the excessive contact causes the cutting edges to become dull relatively rapidly.
It has long been recognized by those skilled in this art that the hand grinding of the inside faces of the shank portions by skilled artisans was one of the most time consuming and thus expensive operations involved in the manufacture of scissors, shears and like tools.
One alternative to the hand grinding operation was proposed in Vogel U.S. Pat. No. 4,133,107. That patent discloses a cutting tool having a bearing dimple formed on the inside face of one of the shank portions. The bearing dimple projects above and from the surface of the inside face of the shank portion and contacts the inside face of the other shank portion as the cutting tool is moved from an open to a closed position. Contact with the bearing dimple biases the one ends of the members apart, about the connection point, so that there will be "point contact" between the cutting edges of the two members. A molded bearing projection similar to that disclosed in the Vogel patent is disclosed in Nishikawa U.S. Pat. No. 4,250,620. While the Vogel bearing dimple concept works very well for creating the bias of the cutting edges about the connection point, its uniform height can not create sufficient bias at the distal ends of the members to enable the cutting tool to have a light feel, or what is known in the art as a "Japanese feel."
Another alternative to the hand grinding operation was proposed in Hembling U.S. Pat. No. 4,420,884. That patent discloses a scissors having control cams stamped on each shank portion of the scissors. The cams are in sliding contact over one another and cause the planes of the blades to tilt relative to one another so that the cutting portions of the blades are in contact, and so that there is point contact along the cutting edges as the blades are closed. Although the Hembling concept of surface to surface camming action permits point contact of the cutting edges, it also results in a "sticky or gummy" feel that requires increased cutting force.
Cutting tools having a light or "Japanese feel" have been increasingly in demand, particularly by those who use a cutting tool extensively during the work day, since very little cutting force is needed to operate such tools. "Japanese feel" cutting tools are relatively expensive due to the tremendous amount of hand work that must be done to precisely grind the surface of the shank portions. More specifically, the shank portions of the "Japanese feel" tools must be ground so that there is sufficient bias at the distal ends of the members to obtain the desired light feel, yet not so much that the point of contact only occurs when the blade portions are moved to their closed position.